Compare WP Custom Field date

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Take a look at meta.php:777:

... CAST($alias.meta_value AS {$meta_type}) {$meta_compare} {$meta_compare_string})...

So if you want to use DATE comparisons, you should use MySQL compatible date formats (YYYY-MM-DD).

Change this part of your code:

array(
    'key' => 'date',
    'value' => date("Y/m/d"),
    'compare' => '>=',
    'type' => 'DATE'
),

to:

array(
    'key' => 'date',
    'value' => date("Y-m-d"),  // <- change
    'compare' => '>=',
    'type' => 'DATE'
),

and it should work just fine.